Method for the monitoring and treatment of spontaneous cardiac arrhythmias

ABSTRACT

An implantable apparatus for the detection and monitoring of spontaneous cardiac electrogram features in a comprises a cardiac monitoring device and a plurality of subcutaneous cardiac sensing electrodes electrically connected to the monitoring device. The sensing electrodes are configured for sensing cardiac electrogram features when implanted in spatially separate locations in a patient. A storage device contained within the monitoring device is operably associated with the subcutaneous electrodes and stores the cardiac electrogram features. Preferably, the plurality of subcutaneous electrodes are carried by a single elongate lead. A downloading device such as telemetry apparatus or transcutaneous electrical connectors may be provided so that the stored information can be downloaded to a separate apparatus external to the patient. In a preferred embodiment, the apparataus is a defibrillator. Methods of using such apparatus are also disclosed.

FIELD OF THE INVENTION

The present invention relates to an implantable device that monitorscardiac electrogram feature information, which information can be usedto detect and predict the onset of spontaneous cardiac arrhythmias. Theelectrogram feature information is detected through subcutaneouselectrodes. The device can incorporate a defibrillator or othertherapeutic shock treatment apparatus for treating cardiac arrhythmias.

BACKGROUND OF THE INVENTION

Numerous different cardiac arrhythmias are treated through implantabledevices. Arrhythmias that can be treated with such devices includeatrial and ventricular fibrillation, as well as less pronouncedarrhythmias. Since such devices typically contain their own powersupply, it is desireable to accurately predict when a therapeuticelectrical pulse should be administered so that unnecessary pulses canbe avoided. It is also desireable to be able to predict arrythmias inadvance of onset or at an early phase, before the arrythmia progressesto a serious stage such as ventricular fibrillation. Accordingly, almostall implantable arrhythmia treatment devices incorporate sensingelectrodes and sensing circuitry.

Current sensing electrodes are positioned on the right side of theheart, at the end of the defibrillation lead. Such sensing electrodescollect little information on electrical activity in the left ventricle.Because most arrhythmias originate in the left ventricle, obtaining leftventricle electrical information is highly desireable to providing anindication of risk of arrhythmia. In addition, spatial distribution ofsensing electrodes (i.e., separating the electrodes in differentlocations) is also important, because spatially separate electrodesgather information from a greater volume of heart tissue. But, it isundesireable to place an electrode in the left ventricle because of therisk of clott formation on the catheter, leading to stroke.

In view of the foregoing, there is a continued need for new sensingelectrode configurations and techniques that can be employed inimplantable arrhythmia treatment apparatus.

SUMMARY OF THE INVENTION

A first aspect of the present invention is an implantable apparatus forthe detection and monitoring of spontaneous cardiac electrogram featuresin a patient. In a preferred embodiment, the apparatus is adefibrillator. The apparatus comprises an implantable cardiac monitoringdevice and a plurality of subcutaneous cardiac sensing electrodeselectrically connected to the monitoring device. The sensing electrodesare configured for sensing cardiac electrogram features when implantedin spatially separate locations in a patient. A storage device containedwithin the monitoring device is operably associated with thesubcutaneous electrodes and stores the cardiac electrogram features.Preferably, the plurality of subcutaneous electrodes are carried by asingle elongate lead. A downloading device such as telemetry apparatusor transcutaneous electrical connectors may be provided so that thestored information can be downloaded to a separate apparatus external tothe patient.

A second aspect of the present invention is a method for detectingcardiac electrogram features in a patient in need thereof. The methodcomprises providing a plurality of subcutaneous sensing electrodesimplanted in spatially separate locations in the patient, providing animplantable cardiac monitoring device operably associated with thesubcutaneous sensing electrodes, detecting cardiac electrogram featuresthrough the plurality of sensing electrodes, and then storing thedetected cardiac electrogram features in the monitoring device. Thedetected information can be used to administer an appropriatetherapeutic electrical pulse to the patient.

The foregoing and other objects and aspects of the present invention areexplained in detail in the drawings herein and the specification setforth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an apparatus of the present invention as implanted inthe thorax of a patient;

FIG. 2 illustrates a cardiac waveform, with the various components andfeatures thereof that may be detected in accordance with the presentinvention;

FIG. 3A schematically illustrates a differential amplifier that isconnected to sensing electrodes of FIG. 1 in a prior art configuration;

FIG. 3B schematically illustrates differential amplifiers that areconnected to sensing electrodes of FIG. 1 in various configurations ofthe present invention; and

FIG. 4 schematically illustrates an apparatus of FIG. 1, showing therelationship between various circuits.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The terms "defibrillator", defibrillate" and defibrillation as usedherein are intended to encompass cardioverter, cardiovert, andcardioversion, along with any other methods and apparatus that providefor a therapeutic treatment pulse to the heart of a subject, such aspacer, pace, pacing.

The term "subcutaneous" as used herein means outside the rib cage, andoutside the chest cavity. In general, subcutaneous sensing electrodesdescribed herein are positioned on the thorax of the patient, preferablyon the left side and on the ventral surface (that is, on the chest). Thesubcutaneous electrodes may be carried by the same lead or differentleads (preferably the same). The electrodes are preferably positioned ator below the level of the collar bone, and at or above the level of thexiphoid process, and are preferably positioned on the left side of thethorax.

The term "treatment pulse" as used herein refers to any type oftreatment pulse, including low energy treatment pulses (e.g., under 8joules for ventricular pulses; under 4 joules for atrial pulses) andhigh energy treatment pulses (e.g., 8 joules or more for ventricularpulses; 4 joules or more for atrial pulses). The pulses may be in pacingpulses including antitachycardia pacing, cardioversion pulses,defibrillation pulses, etc. The pulses may be delivered in any formincluding single or multiple pulses, sequential pulses, pulse trains,combinations thereof, etc.

The phrase "likelihood of occurrence of a spontaneous cardiacarrhythmia" is intended to include both situations where a cardiacarrhythmia has not yet occurred but is likely to occur in the future,and where a cardiac arrhythmia has occurred and is continuing.

An apparatus of the present invention is schematically illustrated inFIG. 1. The apparatus is illustrated implanted in the thorax 2 of apatient. As illustrated, the apparatus includes an implantable cardiacdefibrillator 18 which serves as the implantable cardiac monitoringdevice. An elongate lead 20 carrying two subcutaneous cardiac sensingelectrodes 22, 24 is electrically connected to the defibrillator, withthe sensing electrodes configured for sensing cardiac electrogramfeatures when implanted in spatially separate locations in a patient.The elongate lead includes a defibrillation electrode 26, which isoptional but preferred.

The defibrillator is configured for implantation in the leftpre-pectoral position, and the elongate lead is configured for extendingfrom the xiphoid process of the sternum of the patient to theimplantable cardiac arrhythmia monitoring device. In general,subcutaneous electrode 24 is configured on the lead for positioningadjacent the xiphoid process of the patient, and subcutaneous electrode22 is configured on the lead for positioning adjacent the left axilla ofthe patient. Additional subcutaneous sensing electrodes positioned onthe lead proximal and/or distal to electrode 22 may be included ifdesired, and additional defibrillation electrodes may be positioned onthe lead both proximal and/or distal to defibrillation electrode 26.

An elongate transveneous catheter 11 connected to the defibrillator 18by yoke 15 to single conductors 12, 14 is flexibly configured forinsertion into the heart 4 of the patient through the right atrium 7 andinto the right ventricle 6. The catheter carries a distal, rightventricle electrode 8 and a proximal electrode 10. The proximalelectrode 10 may be configured for positioning in any suitable location,such as the right atrium or superior vena cava. An additional, rightatrium pacing and sensing electrode 28 is also illustrated, whichelectrode is optional but preferred. In general, at least onedefibrillation electrode is included on the transveneous catheter, whichmay be inserted into the right atrium, the right ventricle, the coronarysinus or a peripheral vein, etc. The defibrillation pulse is preferablyadministered by one or more pair of electrodes: the complementaryelectrode (or additional electrodes) may be positioned in any suitablelocation, such as on the same or a different transvenous catheter, as apatch electrode on the outer surface of the heart, on the outer surfaceof the defibrillator (an "active can" electrode), on the lead carryingthe subcutaneous sensing electrodes, etc.

The circuitry within housing 18 is schematically illustrated in FIG. 4.A detection circuit is electrically connected to the sensing electrodes22, 24 by lines 22', 24', and the defibrillation electrodes 8, 10, 26are electrically connected to the pulse circuit 43 by lines 8', 10' 26'.The detection circuit may include or incorporate a cardiac electrogramfeature detector, including but not limited to QT interval detectors, PRinterval detectors, ST interval detectors, RT interval detectors, T waveduration detectors, QRS duration detectors, R wave morphology detectors,and T wave morphology detectors (various features being illustrated bythe representative cardiac electrogram set forth as FIG. 2). Thedetection circuit 41 is operably associated with control circuit 42,which is in turn associated with the pulse circuit 43 for delivering atreatment pulse through the defibrillation electrodes. Numerousdifferent detection circuitries are known, and may be employed ormodified to carry out the present invention. See, e.g., U.S. Pat. Nos.5,560,369; 5,447,519; 5,314,430; 5,366,486; and 5,620,471(thedisclosures of which are incorporated herein by reference). The pulsecircuit typically includes a capacitor and capacitor charger, as isknown in the art.

In the embodiment illustrated in FIG. 1, the treatment pulse would be aventricular defibrillation pulse, but any other type of treatment pulseas discussed above could be delivered, through the same or a differentelectrode configuration (as also discussed above).

A memory circuit 44 serving as a storage means is contained within thedefibrillator and is operably associated with the sensing electrodesthrough the control circuit 42 for storing the cardiac electrogramfeatures, and is operably associated with a telemetry circuit 45. Thedetection circuit 41 may be considered as part of the storage means inthe illustrated embodiment, but is not critical thereto. In general, anymemory device or circuit with or without a corresponding detectioncircuit and intervening processing circuit may serve as the storagemeans. The electrical activity may be stored in analog or digital form;the electrical activity may be stored as raw electrical data or asfeatures or information derived from raw electrical data. The memory andtelemetry circuits can be implemented in accordance with knowntechniques (see, e.g., U.S. Pat. No. 5,560,369).

Any suitable sensing electrode configuration can be employed with thedetector, with at least one and preferably at least two sensingelectrode carried by the subcutaneous lead(s). FIG. 3A illustrates anelectrode configuration of the prior art, in which electrodes 8 and 10are employed in the illustrated position as the sensing electrodes. Inthe present invention, suitable electrode configurations for the sensingelectrodes include electrodes 24 and 8; electrodes 22 and 8; electrodes24 and 22; electrodes 24 and 18; and electrodes 22 and 18. Wheredefibrillator 18 is designated as the electrode, the electrode is on theouter surface of the defibrillator (referred to as an "active can"electrode). Polarity is not critical and may be reversed from thatindicated.

The defibrillator may also include a telemetry circuitry 45 (see FIG. 4)or tanscutaneous electrical connectors that serve as downloading meansoperatively associated with the storage means for transferring storedinformation on the electrical activity of the heart of the patient fromthe implantable cardiac arrhythmia monitoring device to a separateapparatus external to the patient. Thus the present invention can beused to detect arrhythmia, and then download feature and arrhythmiainformation and conduct an analysis to identify features that correlatewith the onset of arrhythmia. The information can be used to reprogramor modify the device, or the device may auto-learn over time.

As will be appreciated by those skilled in the art, numerous circuitryconfigurations may be employed. The power supply may include a singlecapacitor, and the control circuit may be configured so that multiplecomponents of the pulse are generated by the discharge of the singlecapacitor. The power supply may include a first and second capacitor,with the control circuit configured so that multiple components of thepulse are generated by the discharge of different capacitors. Multiplecapacitors may be yoked together.

Systems as described above may be implanted in a patient by conventionalsurgical techniques, or techniques readily apparent to skilled surgeonsin ligyht of the disclosure provided herein, to provide an implantedsystem.

Additional features can be added to the invention without affecting thefunction of the invention and result thereof. Such additional featuresinclude, but are not limited to, safety features such as noisesuppression or multiple wave monitoring, verification checking to reducefalse positives, precardiioversion warning, programmed delayedintervention, bipolar configured sensing electrodes, intermittentlyactivated defibrillation detection to reduce energy drain, switching tominimize lines from the pulse generator, etc.

In use, the apparatus described above provides a therapeutic method thatincludes detecting cardiac electrogram features in a patient in needthereof. In overview, the method comprises providing a plurality ofsubcutaneous sensing electrodes implanted in spatially separatelocations in the patient; providing an implantable cardiac defibrillatoroperably associated with the subcutaneous sensing electrodes; detectingcardiac electrogram features through the plurality of sensingelectrodes; providing at least one elongate transveneous catheterinserted into the heart of the patient, the catheter connected to thedefibrillator and carrying at least one defibrillation electrode;detecting electrical activity of the heart of the patient through thesubcutaneous sensing electrodes; determining the likelihood of aspontaneous cardiac arrhythmia from the detected electrical activity;and then administering a therapeutic pulse to the heart through the atleast one defibrillation electrode upon the determination of alikelihood of occurrence of a spontaneous cardiac arrhythmia. As above,the therapeutic pulse may be an atrial or ventricular therapeutic pulse.The method may further comprise the step of storing the detected cardiacelectrogram features in the defibrillator, and then downloading thestored electrical activity to an external device. The stored electricalactivity may be analyzed following the downloading step, and atherapeutic recommendation generated for managing cardiac arrhythmia forthe patient based on the stored, downloaded, electrical activity.

The foregoing is illustrative of the present invention, and is not to beconstrued as limiting thereof. The invention is defined by the followingclaims, with equivalents of the claims to be included therein.

What is claimed is:
 1. A method for detecting cardiac electrogramfeatures in a patient in need thereof, comprising:providing a pluralityof subcutaneous sensing electrodes implanted in spatially separatelocations in said patient, wherein said plurality of subcutaneouselectrodes are carried by a single elongate lead; providing animplantable cardiac monitoring device operably associated with saidsubcutaneous sensing electrodes; detecting cardiac electrogram featuresthrough said plurality of sensing electrodes; and storing said detectedcardiac electrogram features in said monitoring device to provide storedelectrical activity; and extending said elongate lead from the xiphoidprocess of the sternum of said patient to a cardiac monitoring deviceimplanted in the left pre-pectoral position in said patient.
 2. A methodaccording to claim 1, further comprising the step of downloading saidstored electrical activity to a separate apparatus external to saidpatient.
 3. A method according to claim 2, further comprising the stepsof:analyzing said stored electrical activity following said downloadingstep; and then generating a therapeutic recommendation for managingcardiac arrhythmia for said patient based on said stored electricalactivity.
 4. A method according to claim 1, further comprisingpositioning one of said subcutaneous electrodes adjacent the xiphoidprocess of the patient, and another of said subcutaneous electrodesadjacent the left axilla of the patient.
 5. A method according to claim1, wherein said detecting step comprises the step of detecting an eventselected from the group consisting of QT interval, PR interval, STinterval, RT interval, T wave duration, QRS duration, R wave morphology,and T wave morphology.